I. Field of the Invention
This invention relates to a method of and apparatus for cutting a tube. Specifically, the present invention relates to such a method for cutting a boiler tube in a power generating station and to an apparatus therefor.
II. Description of the Prior Art
A typical power generating station includes one or more generating boilers to generate steam to turn the turbines. Generating boilers are of rather large construction, often reaching several tens of feet in height and involving several hundreds of cubic feet of space. A generating boiler is typically a large steel building-like structure wherein the interior of the steel or brick walls are lined by tube-walls to define a massive interior space. The hollow interior is filled with heat generating material, such as burning coal and the like. The tube-walls of the boiler are formed of hundreds of long, generally vertical steel tubes (e.g. 2-inch tubes, having a wall thickness of about 1/4 inches) which are welded together with long, narrow (e.g. 1/8 or 3/8 inch) strips of steel membrane or web to form a generally sealed container. A typical boiler may include as many as fourteen hundred such tubes. Additionally, in certain areas of the boiler such as in the penthouse or roof area of a boiler, several such steel tubes are present but may not be joined or welded to other tubes such as by a membrane or web and may not present a surface in a plane common to a plurality of tubes. Typically, water is pumped through the tube-walls and single boiler tubes and heated by the burning coal within the building. The heated water is utilized to generate electricity by turning turbines, for example.
Occasionally, it may be necessary to repair or replace a defective portion of a single tube or a plurality of such single tubes in the penthouse, for example. These tubes are free standing in that they are not connected by a web or membrane to an adjacent tube, but they are rigidly held in place within the boiler structure as they form part of an intricate network of plumbing.
To remove the portion of defective tube, one or more workmen using hand-held power saws (or grinders) would make two generally parallel spaced-apart cut lines through the tube. To accomplish these cuts, the workmen would push the edge of a rotating grinding blade against the surface of the tube and move it back and forth and around the tube until the tube is cut or ground through. The use of hand-held power tools in this fashion is both time-consuming and very inaccurate leading to time consuming and costly rework to fit the new section of tube in place. As an example, it takes approximately 33 man-minutes to cut through a typical 2-inch diameter steel boiler tube with a hand-held power saw according the the foregoing method.
Typical of hand-held power saws used for this prior method is a tool referred to as a "Rockwell 90" which is relatively small and uses a small three or four inch cutting or grinding disc. The cut made by the small disc may appear as though it wobbled as it cut due to the inherent inability to maintain a precise line of cut with a hand-held power tool. Of course, use of a larger disc would likely lead to more apparent wobble and may be too dangerous for use according to the method now commonly employed to cut the tube. Further, the workman is likely to veer substantially from the intended cut-line from time to time because of the above limitation inherent in the use of such hand tools. As a result, the cut-line is not straight but has hills and valleys. These hills and valleys must be removed or built up, respectively, to mate the new tube portion with the remaining tube.
The curative steps involved in removing or building-up the tube-wall are very time-consuming, costly and prone to error. For example, a valley would require the use of a small insert referred to as a dutchman. The dutchman must be welded in place between the existing tube and the new tube portion. These added welds take time and increase the chances of making a defective weld. Defective welds would result in rejection of the work by the owner (e.g., the power company) and, hence, costly re-work to correct the error. Additionally, the time consumed in cutting, removing, inserting and reworking tube portions is precious as the power company is likely to be operating at reduced capacity while that generating boiler is being serviced. Hence, it is imperative that removal and replacement of tube portions occur as rapidly as possible. The time currently necessary to make each line of cut, the time-consuming rework and preparation of exposed tube ends after each such cut, and placement/welding of the new portion of tube may well run into hours instead of minutes, all at great cost in down-time to the power company and in wages and related labor expenses. Also, because single-tube repair often occurs in the highest portion of the boiler, the workers are exposed to potentially serious risk for the long time during which they are working on the tube(s). Also, such tubes may often be in difficult-to-reach locations thus making careful, clean cuts all the more difficult.
Some power driven tube cutters have been described such as in U.S. Pat. Nos. 3,704,516 and 2,291,395 to name a couple. However, such devices operate by surroundingly clamping completely about the tube and making a planetary cut about the tube. In the boiler tube environment, such devices are typically of little use for two reasons. First, the tube to be cut is typically positioned very close to the other tubes and/or the wall. Hence, there is insufficient room for the cutter to be rotated about the tube to make a planetary cut. Second, the tube may be so close to another tube or the wall that the clamping structure, such as a chain, cannot surroundingly grasp the tube. Hence, hand-held tools have remained the norm for cutting boiler tubes.
In addition to the above-discussed drawbacks to the use of hand-held power tools, a further drawback is that the cutting or grinding discs wear out frequently. For example, to cut or grind through a 2-inch tube as before-described requires, on average, approximately three and one half discs. That is, on average, for every ten tubes cut, thirty-five discs are expended in the process. As a result, large tool costs are incurred for each tube to be repaired Additionally, several such tools are typically in use (by several workmen) at the same time in an effort to minimize down-time of the boiler. Because a number of the tools must thus be available, tool costs are high. Finally, because the hand-held power saws are relatively small, and there are so many on the job site, they are an easy target for costly pilferage.
Accordingly, it has been one objective of the present invention to provide a method and apparatus for cutting a boiler tube in a power generating station in a few man-minutes thereby greatly reducing labor costs and related labor expenses.
Another objective of the present invention has been to provide a method and apparatus for rapidly cutting a boiler tube with relatively few tools thereby reducing tool costs.
An even further objective of the present invention has been to provide a method and apparatus for cutting a boiler tube which utilizes a relatively small hand tool but which overcomes the inherent limitations of using such a tool.
A still further objective of the present invention has been to provide a method and apparatus for removing a portion of a boiler tube in generally inaccessible or difficult to reach locations.
Another objective of the present invention has been to provide a method and apparatus for removing a portion of a boiler tube in only a few man-minutes, thereby greatly reducing labor costs and related expenses, but which results in exposed tube ends which are easily prepared to receive a new tube portion without extensive rework.
A yet further objective of the present invention has been to provide an apparatus for cutting a boiler tube which apparatus is portable yet has the advantages sought in the method herein.